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Baby girls more likely near the equator
AKIRA LWANAG/EPA/CORBIS
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Shoot 'em up combat is good for your eyesight
Tropics have a penchant for baby girls WOMEN living in tropical latitudes have a greater chance of giving birth to a girl, according to the first global study to link geographical latitude with the sex ratio of births. Normally, slightly more boys are born than girls. Countries at tropical latitudes enjoy warmer temperatures and longer, more constant day lengths, but it’s not clear why their maternity wards are more “girl-rich”, says Kristen Navara of the University of Georgia in Athens. She analysed birth data between 1997 and 2006 from 202 countries collected by the US Central Intelligence Agency. “Of the 20 countries where fewest boys were born, 18 were at tropical latitudes,” she notes. Navara’s analysis of the CIA data suggests that worldwide, boys account for
DOCTORS may start prescribing a dose of violent conflict, if a trial confirms evidence that computer gaming improves eyesight. Six years ago Daphne Bavelier at the University of Rochester, New York, exploded the myth –Girl power– that gaming is bad for your eyes by showing that expert gamers 51.3 per cent of births, with just outperform non-gamers at over 105 boys born for every a variety of visual tasks (New 100 girls. But in tropical countries Scientist, 31 May 2003, p 11). only 51.1 per cent of births are boys. Now she has demonstrated that And in one country, the Central playing action-packed video African Republic, just 49 per cent of games improves a person’s ability births were boys, so more of the to perceive contrast, a skill we newborns were actually girls. rely on in dark conditions. Although the differences appear The finding raises the prospect small, they translate into thousands of that people with amblyopia, which babies every year, says Navara, whose affects contrast perception, could results appear in Biology Letters (DOI: 10.1098/rsbl.2009.0069). In the Central African Republic, for example, 1400 fewer boys were born in 2006 than if the sex ratio had been 50:50. Other “girl-rich” tropical countries included Grenada, Mauritius and Bermuda. Navara says the results echo those of other studies in mammals, including meadow voles and Siberian hamsters, which have fewest males when days are shortest. She thinks variation in the circadian hormone melatonin is a factor, but there’s no clear explanation. Andy Coghlan ■
“The study is the first indication that contrast perception can be altered without corrective lenses” be treated with games. A trial has begun to test that theory. Amblyopia, sometimes known as “lazy eye”, affects around 3 per cent of people in western populations and happens when the brain fails to correctly register signals from one eye. It can be treated in children but often goes undetected until adulthood,
when there is no established fix. Bavelier’s team randomly assigned 13 healthy young adults, who did not previously play video games, to play either action games like the first-person shooter Unreal Tournament or more sedate titles such as The Sims, for 50 hours over nine weeks (Nature Neuroscience, DOI: 10.1038/nn.2296). Tests before and after showed that the contrast perception of both groups improved. But the action-game group showed 43 per cent improvement on average, compared with just 11 per cent in the other group. The effect persisted for months, even when people didn’t play games at all. The study is the first indication that contrast sensitivity can be altered without corrective lenses or surgery, says Bavelier. Her work has inspired Dennis Levi and colleagues at the University of California, Berkeley, to begin a trial to see whether gaming can help people with amblyopia. Bavelier’s results show gaming’s potential for clinical treatment, says Lotfi Merabet, a neuroscientist at the Beth Israel Deaconess Medical Center in Boston, who uses games for visual rehabilitation. He predicts gaming will become a common clinical tool. Alison Motluk ■
4 April 2009 | NewScientist | 11
For daily news stories, visit www.NewScientist.com/news
Shoot 'em up combat is good for your eyesight
Tropics have a penchant for baby girls WOMEN living in tropical latitudes have a greater chance of giving birth to a girl, according to the first global study to link geographical latitude with the sex ratio of births. Normally, slightly more boys are born than girls. Countries at tropical latitudes enjoy warmer temperatures and longer, more constant day lengths, but it’s not clear why their maternity wards are more “girl-rich”, says Kristen Navara of the University of Georgia in Athens. She analysed birth data between 1997 and 2006 from 202 countries collected by the US Central Intelligence Agency. “Of the 20 countries where fewest boys were born, 18 were at tropical latitudes,” she notes. Navara’s analysis of the CIA data suggests that worldwide, boys account for
DOCTORS may start prescribing a dose of violent conflict, if a trial confirms evidence that computer gaming improves eyesight. Six years ago Daphne Bavelier at the University of Rochester, New York, exploded the myth –Girl power– that gaming is bad for your eyes by showing that expert gamers 51.3 per cent of births, with just outperform non-gamers at over 105 boys born for every a variety of visual tasks (New 100 girls. But in tropical countries Scientist, 31 May 2003, p 11). only 51.1 per cent of births are boys. Now she has demonstrated that And in one country, the Central playing action-packed video African Republic, just 49 per cent of games improves a person’s ability births were boys, so more of the to perceive contrast, a skill we newborns were actually girls. rely on in dark conditions. Although the differences appear The finding raises the prospect small, they translate into thousands of that people with amblyopia, which babies every year, says Navara, whose affects contrast perception, could results appear in Biology Letters (DOI: 10.1098/rsbl.2009.0069). In the Central African Republic, for example, 1400 fewer boys were born in 2006 than if the sex ratio had been 50:50. Other “girl-rich” tropical countries included Grenada, Mauritius and Bermuda. Navara says the results echo those of other studies in mammals, including meadow voles and Siberian hamsters, which have fewest males when days are shortest. She thinks variation in the circadian hormone melatonin is a factor, but there’s no clear explanation. Andy Coghlan ■
“The study is the first indication that contrast perception can be altered without corrective lenses” be treated with games. A trial has begun to test that theory. Amblyopia, sometimes known as “lazy eye”, affects around 3 per cent of people in western populations and happens when the brain fails to correctly register signals from one eye. It can be treated in children but often goes undetected until adulthood,
when there is no established fix. Bavelier’s team randomly assigned 13 healthy young adults, who did not previously play video games, to play either action games like the first-person shooter Unreal Tournament or more sedate titles such as The Sims, for 50 hours over nine weeks (Nature Neuroscience, DOI: 10.1038/nn.2296). Tests before and after showed that the contrast perception of both groups improved. But the action-game group showed 43 per cent improvement on average, compared with just 11 per cent in the other group. The effect persisted for months, even when people didn’t play games at all. The study is the first indication that contrast sensitivity can be altered without corrective lenses or surgery, says Bavelier. Her work has inspired Dennis Levi and colleagues at the University of California, Berkeley, to begin a trial to see whether gaming can help people with amblyopia. Bavelier’s results show gaming’s potential for clinical treatment, says Lotfi Merabet, a neuroscientist at the Beth Israel Deaconess Medical Center in Boston, who uses games for visual rehabilitation. He predicts gaming will become a common clinical tool. Alison Motluk ■
4 April 2009 | NewScientist | 11